Field of the Invention
This invention relates, generally, to vehicle ice and chain traction systems which may be both rapidly deployed and rapidly retracted. More particularly, it relates to an actuator apparatus in which a pneumatic cylinder linearly motivates a slidable rack comprised of equally-spaced, parallel roller pins mounted thereon. The roller pins engage a rotatable sprocket that is coupled to a chain traction system deployment arm.
Description of Related Art
Rapidly-deployable chain traction systems, which may be characterized generally as systems which fling short chain or cable segments beneath a road tire, have been known for some 90 years. Such a system is disclosed in U.S. Pat. No. 1,045,609 and in German Pat. No. 266,487 to W. H. Putnam for an ANTISKIDDING DEVICE. Throughout the years, various modifications and improvements have been made by numerous inventors. The following list is a representative list of a dozen other U.S. patents issued in this field:                U.S. Pat. No. 1,150,148 for a TRACTION AND ANTISKIDDING DEVICE;        U.S. Pat. No. 1,223,070 for an ANTISKIDDING DEVICE FOR VEHICLES;        U.S. Pat. No. 1,374,252 for an ANTISKID DEVICE FOR AUTOMOBILES;        U.S. Pat. No. 1,381,001 for a NON-SKID DEVICE FOR MOTOR AND OTHER VEHICLES;        U.S. Pat. No. 1,975,325 for an ANTISKID CHAIN AND MEANS FOR APPLYING AND REMOVING SAME;        U.S. Pat. No. 2,241,923 for an AUTOMATIC EMERGENCY TRACTION DEVICE FOR AUTOMOBILES;        U.S. Pat. No. 2,264,466 for an ANTISKID DEVICE FOR VEHICLES;        U.S. Pat. No. 2,277,036 for an ANTISKID DEVICE;        U.S. Pat. No. 2,283,948 for an AUTOMOBILE TRACTION DEVICE;        U.S. Pat. No. 2,442,322 for an ANTISKID DEVICE;        U.S. Pat. No. 4,299,310 for an ANTISKID DEVICE FOR MOTOR VEHICLES;        U.S. Pat. No. 4,800,992 for an ANTI-SKID DEVICE; and        U.S. Pat. No. Des. 286,524 for ANTI SKID CHAIN UNIT FOR VEHICLE TIRES.        
Referring now to the prior-art system of FIG. 1, a modern rapidly-deployable chain traction system 100 is depicted in its deployed configuration in this rear elevational view drawing. The chain traction system 100 is removably affixed to a drive axle 101 which incorporates a differential unit 102. Inner and outer road wheels (103A and 103B, respectively) are mounted on the visible half of the drive axle 101. On each road wheel (103A and 103B) is mounted a rubber tire (104A and 104B, respectively). The chain system 100 includes a friction drive disc 105 to which a plurality of traction chain segments 106A, 106B and 106C (106, generally) are attached. Chain segment 106A is depicted as being below the road surface 114, which is normally covered with a layer of snow or ice when the chain system 100 is in the deployed configuration. The friction drive disc 105 is rotatably mounted on a spindle 107 which is affixed to a deployment arm 108 which is pivotally mounted to a main frame bracket 109. The main frame bracket 109 is, in turn, bolted to the U-bolt shackles 113 which secure the suspension leaf springs 112 to the drive axle 101. The chain system 100 also includes a pneumatic cylinder 110 that is bolted to the main frame bracket 109. The pneumatic cylinder 110 has an internal piston (not shown) that is coupled to a slidable rod 111 that is held in a normally retracted position within cylinder 110 by spring biasing when pressure within cylinder 108 equals ambient pressure. The outer end of slidable rod 111 is connected to deployment arm 108. In the deployed configuration, the outer rim of friction drive disc 105 is pressed against the sidewall of tire 104A by a biasing force applied to deployment arm 108 by slidable rod 111. The biasing force is provided by pneumatic pressure inside pneumatic cylinder 110 which overcomes the spring biasing and causes slidable rod 111 to extend. As the tire 104A rotates, the friction drive disc 105 also rotates with the chain segments 106 extended more or less radially therefrom. Thus each chain segment 106 is flung, sequentially, beneath the tread portion of tire 104A. In order to retract the system and disengage the friction drive disc 105 from contact with the sidewall of tire 104A, pneumatic pressure to pneumatic cylinder 110 is cut off, causing slidable rod 111 to retract within cylinder 110 and raising the deployment arm 108, the rotatably attached friction drive disc 105 and the attached chain segments 106. In the retracted configuration, the chain segments 106 do not touch the road surface 114.
Referring now to FIG. 2, mounting of the rapidly-deployable chain traction system 100 of FIG. 1 to the axle 101 is shown in detail. For the sake of simplicity, the traction chain segments 106 have been removed from the friction drive disc 105. On each side of the vehicle, a chain traction system 100 is secured via a mounting assembly 200 to U-bolt shackles 113 which commonly secure the axle 101 to a set of leaf springs 112 (see FIG. 1). Each leaf spring set is coupled to the beam axle or axle housing (in the case of a live axle) with a pair of U-bolt shackles 113, which are tied together beneath the axle or axle housing with shackle plates 201 that are secured with four standard nuts 202 (two on each U-bolt). The mounting assembly 200 for each side of the vehicle includes four coupling nuts 203 which engage exposed threads on the U-bolt shackles 113, two tie plates 204, which tie together the pairs of U-bolt shackles 113, a tube 205 that is bolted to a center aperture in each tie plate 204, and a link plate 206 that is bolted to both the tube 205 and the main frame member 206 of the chain traction system 100.
Still referring to FIG. 2, it will be noted that slidable rod 111 of the pneumatic cylinder 110 operates directly on the deployment arm 108 of the chain traction system 100. The deployment arm 108 is pivotally secured with a pivot bolt 207 to the main frame bracket 109. As a consequence of direct action of the piston rod 111 on the deployment arm 108, arcuate motion of the deployment arm 108 is limited to about 150 degrees.
Although various mechanical means, such as cables and gears, have been used in the past to deploy chain traction systems, the current genre of chain traction systems relies almost exclusively on pneumatic cylinders for deployment. A major problem associated with chain traction systems deployed by pneumatic cylinders is that the arc of rotation of the support member 108, on which the spindle 107 and friction disc 105 are mounted, is limited to less than about 150 degrees. In addition, the system may be too bulky for certain applications, such as installation on light-duty pickup trucks. One major problem associated with prior art gear-driven deployment systems, on the other hand, is that uneven road surfaces imposed a potentially destructive shock load on the gear train when the chain traction system was in a retracted state. The shock loads had a tendency to shear the teeth off of gears in the deployment gear train. The shock loads could also fracture the housing used to contain the gear train. Another major problem associated with gear-driven deployment systems is that of grit, water, and corrosion related to inadequate protection of the gear train. For a gear-driven deployment system to function reliably, it is essential that all gears and all bearings be completely sealed from the harsh environment beneath the vehicle. Without proper sealing, the life expectancy of such systems would likely be no more than one winter season. Gear driven deployment systems for a chain traction system, if not manually operated, require some type of motor for automatic operation. For most vehicles, the only type of motor that makes sense is an electric motor, as electric power is readily available from the vehicle's storage battery.
U.S. Pat. No. 7,506,729, granted to Fred P. Smith and John H. Atkinson, Jr. on Mar. 24, 2009, titled TORQUE-LIMITED ELECTRIC SERVO SYSTEM FOR DEPLOYING A VEHICLE SNOW CHAIN TRACTION SYSTEM, was an attempt to provide an improved ice chain deployment system where the deployment arm was not limited to rotation through an arc no greater than about 150 degrees. The deployment system, which included a gearbox to which an electric drive motor was externally mounted, required at least one pair of deployment units: one each for right and left drive wheels. Each unit includes a reversible electric drive motor having an armature shaft; an intermediate drive shaft; a worm axially affixed to the intermediate drive shaft; an output shaft; a shock damper affixed to the output shaft; a worm gear affixed to the shock damper, the worm gear meshing with the worm, and providing rotational locking for said output shaft; and a deployment arm coupled to the output shaft, the deployment arm having rotatably mounted thereto a friction drive disc to which were peripherally attached a plurality of chain segments. Torque applied to the output shaft by the electric motor was limited either by a spring-loaded clutch axially mounted on the intermediate drive shaft or by a circuit which limits current drawn by the electric drive motor to a preset maximum. This innovative deployment system, which was initially marketed by the assignee of the present invention, experienced multiple problems, including circuit design problems, water leakage into the circuit components, and a propensity to deploy automatically, which was caused by vibration and shocks experienced by the vehicle on which it was mounted. Though some of the problems were eventually solved, the unit soon gained notoriety as a lemon in the industry, which doomed its acceptance in the marketplace.
What is needed is a new deployment system for a vehicle snow chain traction system that does not suffer from the deficiencies of the heretofore described prior art systems, that is reliable, compact, simple to install, and capable of providing rotational motion in excess of 180 degrees.